Surface mount captive screw ferrule for PCB

ABSTRACT

A method and apparatus for holding a screw captive to a printed circuit board (PCB), with a channel formed through the apparatus and a mounting hole formed through the PCB being in alignment to allow a screw to pass therethrough.

FIELD OF THE INVENTION

The present invention is related to hardware used to mount otherhardware in fixed relation to a printed circuit board (PCB).

Art Background

The vast majority of current day computer systems make use of one ormore printed circuit boards (PCBs) mounted within a computer system'schassis by way of screws protruding through holes formed in those PCBs.However, with such use of screws comes the attendant disadvantage andinconvenience of the screws being loose components.

An increasingly commonplace solution is captive screws, i.e., screwsthat are held captive to the PCB with which they are associated by wayof a captivating component often referred to as a ferrule, or in somecases, referred to as a retainer. A ferrule, or retainer, retains itselfto the PCB, and in turn, retains a screw to the PCB by retaining thescrew to itself. Various forms of ferrules exist, but with variousdrawbacks including risk of damage to the PCB and/or requirements for ahole that is much larger than would actually be required for the screwto be used, alone. A further drawback is that many of the current typesof ferrule protrude through the PCB, and this protrusion can bedifficult to accommodate in various chassis designs. Yet anotherdisadvantage is that at the time the PCB is assembled, the ferruletypically requires a separate step to be installed, thereby adding tothe time and/or cost required when installing components on a PCB (alsocommonly referred to as ‘populating’ a PCB).

BRIEF DESCRIPTION OF THE DRAWINGS

The objects, features, and advantages of the present invention will beapparent to one skilled in the art in view of the following detaileddescription in which:

FIG. 1 is a perspective view of one embodiment of the present invention.

FIG. 2 is a perspective view of another embodiment of the presentinvention.

FIGS. 3 a and 3 b are both combined side and sectional views of stillanother embodiment of the present invention.

DETAILED DESCRIPTION

In the following description, for purposes of explanation, numerousdetails are set forth in order to provide a thorough understanding ofthe present invention. However, it will be apparent to one skilled inthe art that these specific details are not required in order topractice the present invention.

The present invention concerns mounting hardware to mount other hardwareinto a fixed relationship with a PCB. Specifically, the presentinvention concerns using a ferrule (or retainer) mounted to the surfaceof a PCB by way of commonly used surface mount soldering techniques forPCBs. This ferrule is used to hold a screw captive to the PCB for use inmounting the PCB.

FIG. 1 is a perspective view of one embodiment of the present invention.The body of ferrule 110 is comprised of solder flange 112, tube 114 andcapture flange 116. Formed through all three of solder flange 112, tube114 and capture flange 116 is screw channel 118 through which a screw tobe held captive would protrude. On the depicted surface of PCB 150 issolder ring 152 centered about the periphery of mounting hole 158.

Ferrule 110 is shown positioned over PCB 150 such that screw channel 118formed through the body of ferrule 110 is aligned with mounting hole 158of PCB 150. Solder flange 112 provides a soldering extension that comesinto contact with solder ring 152 to fixedly attach ferrule 110 to PCB150 through any of a number of widely known surface mount circuit boardassembly or populating techniques. When ferrule 110 is fixedly attachedto PCB 150, capture flange 116 provides a capture extension that may beused to hold a screw captive to PCB 150 such that the captive screw (notshown) protrudes at least through screw channel 118 when PCB 150 is notmounted, and such that the captive screw protrudes through both screwchannel 118 and mounting hole 158 when PCB 150 is mounted.

FIG. 2 is a perspective view of another embodiment of the presentinvention. In a manner generally corresponding to ferrule 110 of FIG. 1,the body of ferrule 210 is comprised of solder flange 212, tube 214 andcapture flange 216, with screw channel 218 formed through all three ofsolder flange 212, tube 214 and capture flange 216.

Ferrule 210 is shown installed on the surface of PCB 250, ferrule 210having been attached to PCB 250 through any of a number of widely knownsurface mount circuit board assembly or populating techniques. Thoughnot visible in FIG. 2, this use of a widely known surface mount circuitboard assembly or populating technique has resulted in solder flange 212being soldered to a solder ring on the surface of PCB 250, underneathferrule 210. Also not visible in FIG. 2 is that ferrule 210 has beeninstalled at a location on PCB 250 such that screw channel 218 isaligned with a mounting hole formed through PCB 250 (and underneathferrule 210) to form an continuous opening through both ferrule 210 andPCB 250.

Captive screw 230, installed within overmold 220, is shown positionedover ferrule 210 such that captive screw 230 is aligned with screwchannel 218 of ferrule 210 installed on PCB 250. Overmold 220 iscomprised of head 222 and extensions 224. When captive screw 230 isinstalled at least through screw channel 218, extensions 224 of overmold220 engage capture flange 216 of ferrule 210 to hold captive screw 230captive to PCB 250.

Although overmold 220 is depicted as having a distinct head 222 andextensions 224 that engage capture flange 216 of ferrule 210, the exactshape or configuration of overmold 220 can be changed without departingfrom the spirit and scope of the invention as hereinafter claimed.

FIGS. 3 a and 3 b are both combined side and sectional views of stillanother embodiment of the present invention. In a manner generallycorresponding to ferrule 210 of FIG. 2, the body of ferrule 310 of FIGS.3 a and 3 b is comprised of solder flange 312, tube 314 and captureflange 316, with screw channel 318 formed through all three of solderflange 312, tube 314 and capture flange 316.

In both FIGS. 3 a and 3 b, Ferrule 310 is shown installed on the surfaceof PCB 350, ferrule 310 having been attached to PCB 350 through any of anumber of widely known surface mount circuit board assembly orpopulating techniques, resulting in solder flange 312 being soldered tosolder ring 352 on the surface of PCB 350, underneath ferrule 310. Asshown, ferrule 310 has been installed at a location on PCB 350 such thatscrew channel 318 is aligned with mounting hole 358 formed through PCB350 to form a continuous opening through both ferrule 310 and PCB 350.

In both FIGS. 3 a and 3 b, captive screw 330, installed within overmold320, is shown positioned so as to extend through screw channel 318 offerrule 310. Overmold 320 is comprised of head 322 and extensions 324.With captive screw 330 installed, as shown, so as to protrude through atleast screw channel 318, extensions 324 of overmold 320 engage captureflange 316 of ferrule 310 to hold captive screw 330 captive to PCB 350.In FIG. 3 a, captive screw 330 is positioned such that it does notprotrude beyond the side of PCB 350 opposite ferrule 310, which is aposition that captive screw 330 might have prior to PCB 350 beingmounted using captive screw 330. In this position, extensions 324 ofovermold 320 limit the extent to which captive screw 330 may be pulledaway from PCB 350 by engaging capture flange 316 of ferrule 310.

However, in FIG. 3 b, captive screw 330 is positioned such that it doesprotrude beyond the side of PCB 350 opposite ferrule 310, which is theposition that captive screw 330 would have when PCB 350 is mounted usingcaptive screw 330. In this position, the threads of captive screw 330engage whatever hardware is on the side of PCB 350 opposite ferrule 310,and in so doing, the head of captive screw 330 presses ferrule 310against PCB 350, thereby pressing PCB 350 against whatever hardware ison the side of PCB opposite ferrule 310, and PCB 350 is thereby mounted.

As depicted in FIGS. 3 a and 3 b, screw channel 318 formed throughferrule 310 changes diameter part of the way through ferrule 310. Thischange in diameter is made so as to create a ledge about the peripheryof where the diameter is reduced, providing a surface against which aspring (not shown) could be installed at least partly within ferrule310, surrounding the portion of captive screw 330 that protrudes throughscrew channel 318, and pressing either against the underside of theportion of captive screw 330 installed within head 322 of overmold 320or against head 322 of overmold 320, itself. Alternatively, screwchannel 318 could be formed through ferrule 310 with a single andunchanging diameter, and such a spring could be installed against thesurface of PCB 350 that faces ferrule 310. Either way, the installationof such spring could be used to bias captive screw 330 into the positiondepicted in FIG. 3 a when captive screw 330, making this position into apredetermined position for captive screw 330 when captive screw 330 isnot otherwise being used to mount PCB 350. As an alternative to or inaddition to the use of a spring, extensions 324 of overmold 320 could beconfigured to press against the outer surface of tube 314 of ferrule310, thereby causing friction between extension 324 and ferrule 310 thatcould be used to selectively hold captive screw 330 in either of thepositions depicted in FIGS. 3 a and 3 b, or any of a number of positionsin between.

Although solder ring 352 is depicted as being only a ring of solder onthe surface of PCB 350 facing ferrule 310, those skilled in the art willrecognize that mounting hole 358 formed through PCB 350 could be platedthrough with solder with a second solder ring (not shown) on theopposite surface of PCB 350 (i.e., the surface of PCB 350 facing awayfrom ferrule 310). Plating through mounting hole 358 and having such asecond solder ring on the opposite surface of PCB 350 may be done toassist in ensuring a desired electrical connection between a conductorof PCB 350 and the surface to which PCB 350 is mounted using captivescrew 330.

Although captive screw 330 is depicted as having a substantially flathead, those skilled in the art will recognize that the exact shape orconfiguration of captive screw 330 can be changed without departing fromthe spirit and scope of the invention as hereinafter claimed. Also,although overmold 320 is depicted as having a distinct head 322 andextensions 324 that engage capture flange 316 of ferrule 310, the exactshape or configuration of overmold 320 can be changed without departingfrom the spirit and scope of the invention as hereinafter claimed.Furthermore, although captive screw 330 and overmold 320 are depicted aseparate pieces with captive screw 330 installed within overmold 320,those skilled in the art will appreciate that other combinations ofparts could be used to create the equivalent of the combination ofcaptive screw 330 and overmold 320 without departing from the spirit andscope of the invention as hereinafter claimed. Indeed, captive screw 330and overmold 320 may also be fabricated as a single piece.

Although ferrules 110, 210 and 310 have all been depicted as having acapture flange 116, 216 and 316, respectively, that is meant to beengaged as part of holding a screw captive, those skilled in the artwill recognize that one or more of ferrules 110, 210 or 310 may hold ascrew captive using a different shape or configuration that would have adifferent form of capture extension other than capture flange 116, 216or 316. Also, although ferrules 110, 210 and 310 have all been depictedas having a solder flange 112, 212 and 312, respectively, that is meantto provide the surface to be used in surface mounting ferrules 110, 210and 310 to a PCB, those skilled in the art will recognize that one ormore of ferrules 110, 210 or 310 may have a different form of solderingextension using a different shape or configuration that would providesufficient soldering surface area to enable surface mounting to a PCB.

The invention has been described in conjunction with the preferredembodiment. It is evident that numerous alternatives, modifications,variations and uses will be apparent to those skilled in the art inlight of the foregoing description. Although the invention has beendiscussed repeatedly as being used in conjunction with a substantiallycylindrical and tubular ferrule (or retainer), it will be understood bythose skilled in the art that the present invention may be practiced inconjunction with ferrules of other shapes and configurations.Furthermore, although the example embodiments of the present inventionare described in the context of holding a screw captive to a PCB, thepresent invention may be practice in conjunction with holding othertypes of fasteners or other hardware captive to a PCB.

1-8. (canceled)
 9. An apparatus, comprising: a ferrule having a bodywith a channel formed therethrough from a first end of the body having acapture extension, to a second end of the body having a solderingextension in the form of a solder flange formed thereon prior to thecoupling of the ferrule to a printed circuit board providing a solderingsurface to solder the ferrule to a first surface of the material of theprinted circuit board, itself, at a location that aligns the channelformed through the ferrule with a mounting hole formed through the firstsurface and the material of the printed circuit board, itself; and ascrew protruding through the channel formed through the ferrule and heldcaptive to the ferrule by the capture extension.
 10. The apparatus ofclaim 9, wherein the ferrule is substantially cylindrical in shape. 11.The apparatus of claim 9, wherein the capture extension is a captureflange surrounding the channel formed through the ferrule at the firstend.
 12. The apparatus of claim 9, wherein the screw is comprised of ahead installed within an overmold having at least one extension thatengages the capture extension, and that cooperates with the captureextension to hold the screw captive to the ferrule. 13-14. (canceled)15. The apparatus of claim 9, wherein the ferrule is used in cooperationwith the screw protruding through both the channel formed through theferrule and the mounting hole formed through the first surface andmaterial of the printed circuit board, itself, to mount the printedcircuit board.
 16. The apparatus of claim 15, wherein a spring ispositioned within the channel formed through the ferrule to bias thescrew into a predetermined position when the screw is not being used tomount the printed circuit board.
 17. A method comprising: soldering aferrule, having a body with a channel formed therethrough from a firstend of the body having a capture extension to a second end of the bodyhaving a soldering extension in the form of a solder flange providing asoldering surface, to a first surface of the material of a printedcircuit board by the solder flange of the ferrule at a location on thefirst surface where the channel formed through the ferrule aligns with amounting hole formed through the first surface and the material of theprinted circuit board itself, inserting a screw through the channelformed through the ferrule; and using the capture extension to hold thescrew captive to the ferrule.
 18. The method of claim 17, whereinsoldering the ferrule comprises using a surface mount populatingtechnique to solder the soldering extension to the material of theprinted circuit board, itself.
 19. (canceled)
 20. The method of claim17, further comprising using the screw protruding through both thechannel formed through the ferrule and the mounting hole formed throughthe material of the printed circuit board itself to mount the printedcircuit board.
 21. The method of claim 20, further comprisingpositioning a spring within the channel formed through the ferrule tobias the screw into a predetermined position when the screw is not beingused to mount the printed circuit board.
 22. The method of claim 17,wherein the screw is comprised of a head installed within an overmoldhaving at least one extension that engages the capture extension, andthat cooperates with the capture extension to hold the screw captive tothe ferrule.